Modern Engineering Thermodynamics

13.2 Part I. Engines and Vapor Power Cycles 453
WHO WAS JAMES WATT?
James Watt (1736–1819) was a young Scottish machinist at the College of Glasgow and, in 1764, was given the job of
repairing a classroom teaching scale model of a Newcomen engine. The engine was not actually broken. Its problem
was that it consumed so much steam that its boiler was empty after only a few cycles of operation and consequently
it soon stopped running. Watt discovered that this was due to the alternate heating and cooling of the piston-cylinder
unit during the condensation and reheat portions of each cycle. Part of the thermal energy contained in the steam
hadtobeusedtoreheatthepistonandcylinderafterthecondensation process was brought about by the cold water
jet. This energy therefore became unavailable for doing mechanical work. The small size of the scale model engine
had magnified this effect to the point where the engine was soinefficientthatitwouldrunforonlyafewcycles
before using up all the steam available in the boiler. 4 Several months later, he realized that, if the steam was
condensed not inside the piston-cylinder unit, but outside of it in a separate condenser chamber, then the piston and
cylinder could be continuously kept at the high temperature of the steam. This way, the piston-cylinder unit would
not have to be reheated during each cycle of the engine and the steam consumption would be greatly reduced. From
this simple observation was born one of the most significant technological innovations of the 18th century, the
separate steam condenser.
With the addition of a condenser unit, the efficiency of a full-size Newcomen engine was increased several-fold. This
meant that these engines could be reduced in size somewhat (most Newcomen engines at that time were as big as a
two-story house) and adapted to other uses than pumping water out of flooded mines. The smaller Watt engines
provided the medium-scale power sources necessary to bring about the onset of centralized manufacturing, which was
the beginning of the Industrial Revolution. How Watt added a separate condenser to a standard Newcomen pumping
engine is shown in Figure 13.4.
Walking beam
Jacketed steam
cylinder
Valve
rod
Haystack
boiler
Double−acting
piston
To the
boiler
Valves
Pump rod
Condensate
pump
Hot
well
To
mine
pump
Fire
Condenser
Condenser
cooling water
FIGURE 13.4
Watt’s condenser added to a Newcomen pumping engine. Automatic valves alternately admit steam from the boiler to the proper
side of a double-acting piston inside a steam jacketed cylinder, then into a separate condenser unit.
In 1775, Watt entered into a business partnership with the British industrialist Matthew Boulton (1728–1809) for the
purpose of manufacturing his version of the external condenser Newcomen engine. Boulton provided the financial support
(and consequently took two thirds of the patent rights) and Watt was responsible for the engineering and manufacturing
activities.
(Continued)